MU-OPIOID AND KAPPA-OPIOID RECEPTOR-MEDIATED OPIOID EFFECTS ON SOCIALPLAY IN JUVENILE RATS

Previously, morphine has been shown to influence social play behavior in rats on two levels. An increasing effect on social play was interpr eted as an effect on the rewarding aspects of social play. A lower dos e of morphine abolished the effects of an unfamiliar environment on so cial play, supposedly by affecting the integration of environmental st imuli. In the present study the effects of receptor-specific opioid dr ugs on social play and measures of social behavior unrelated to play w ere investigated. Fentanyl, a mu-opioid receptor agonist, seemingly mi micked both effects of morphine. The mu-opioid receptor antagonist, be ta-funaltrexamine, decreased social play, although a low dose of this drug increased it. BUBUC (Tyr-D-Cys(StBu)-Gly-Phe-Leu-Thr(OtBu)) and n altrindole, a delta-opioid receptor agonist and delta-opioid receptor antagonist, respectively, had no effects on social behavior. The kappa -opioid receptor agonist, U50,488H [2-(1-pyrrolidinyl)-cyclohexyl]-ben zeneacetamide), dose dependently suppressed all measures of social beh avior. The kappa-opioid receptor antagonist, nor-binaltorphimine, abol ished the effects of an unfamiliar environment on social play. These s tudies suggest that the opioidergic effect on social play is mediated through mu- and kappa-opioid receptor systems.